How to add a new UV map to all selected objects?
You can get rid of the uv_texture_add() operator by adding a new UVLoopLayer:

import bpy

for obj in bpy.context.selected_objects:
    # Make sure this is a mesh object and that it doesn't already use this UV Map
    if obj.type == 'MESH' and "UV_ao" not in obj.data.uv_layers:
        obj.data.uv_layers.new(name="UV_ao")